The special "eco" versions of small cars such as the Chevrolet Cruze, Ford Focus and Honda Civic don't improve fuel economy enough to be worth the extra money, according to an analysis by Consumer Reports.

The magazine said it could take as long as 38 years for the extra cost to be worthwhile, depending on the vehicle. The cars, which come equipped with special low rolling resistance tires and aerodynamic features, generally cost $500 to $800 more than fuel-efficient siblings that don't carry the "eco" label.

The magazine also evaluated the new Toyota Prius C subcompact hybrid, which has been selling well. Consumer Reports said the Prius C's "stellar 37 mpg in the city is the best of any car" it has tested.

But except for fuel economy and easy parking, Consumer Reports didn't like much else about the vehicle, which has a sticker price that starts at just under $19,000.

"Overall, drivers will get what they pay for," the magazine said. "This subcompact hatchback, which is related to the lackluster Toyota Yaris, suffers from a stiff ride, very noisy cabin, slow acceleration and cheap-looking interior trim."